The present invention relates to the construction of a household fan. More particularly, the present invention relates to a household box fan having an industrial-standard narrow width provided with an improved motor, motor housing and mounting assembly.
Various types of household fans are currently used for cooling and ventilation. Such fans are available in a variety of shapes and sizes. Household fans typically used by consumers have an electric motor used to drive propeller-type blade assemblies. Such fans commonly employ electric motors of the type known as shaded pole motors. One common type of household fan is the xe2x80x9cbox fanxe2x80x9d which generally includes an electric motor and fan blade assembly mounted in a casing that has an overall generally square configuration. Typical box fans usually have a metal frame having front and rear grills, fan control switches and/or knobs, and an exposed handle disposed on the outer surface of the casing. The electric motor is typically mounted in the center of the casing between the two grills. The motor is often mounted to some internal strut members, typically appearing as an elongated metal member that spans from one side of the casing to an opposed side of the casing.
One common type of box fan, often referred to as a xe2x80x9cnarrow bodyxe2x80x9d box fan, has a casing width of approximately 3.75 inches. The narrow thickness of this type of box fan is advantageous for numerous reasons, including low cost of casing materials, narrow width for fitting into window openings, lighter weight, and possible reduction in the overall packaging size. Because of the narrow width of this type of box fan, however, manufacturers are limited as to the space allowed for mounting a motor and fan assembly. Therefore, the electric motor used in these types of box fans is a shaded pole motor, which is compatible with 3xc2xe inch box fans because they provide the necessary power to drive the blade assembly, and yet have a narrow profile capable of fitting within the permitted mounting area within the narrow casing.
However, shaded pole motors tend to be in limited supply since they require large casings which are formed by a punch press with an expensive progressing die, or with multiple punch press operations. Such casings also require an expensive painting step. Such casings are not easily die cast due to their large diameters. In addition, shaded pole motors require laminations which use low carbon steel and must pass through an expensive heat treating step. Supply of these high quality laminations is presently limited. Furthermore, shaded pole motors are inefficient, much of their input energy being lost to undesirable heat generation. In addition to the expense of the laminations, shaded pole motors require epoxy to insulate the stator, the stator is large, the windings require expensive machinery to create, and a punch press with a long feeder is required to create the large diameter casings.
Electric motors are categorized by Underwriters"" Laboratory (UL) according to the difference between their operating temperatures and the ambient temperature. Motors having operating temperatures from 75xc2x0 C. to 95xc2x0 C. above ambient temperature are categorized as Class B, and require special insulation materials. Those motors which operate at temperatures not more than 75xc2x0 C. above ambient temperature are categorized as Class A, and have less stringent requirements for insulation materials. The operating temperatures of many motors are typically more than 75xc2x0 C. above ambient temperature, and therefore, require expensive Class B insulation materials.
One type of electric motor which can be manufactured at lower cost is a four-pole permanent-split capacitor (PSC) motor. PSC motors incorporate a capacitor in series with an auxiliary: coil, the auxiliary coil being connected in parallel with a main coil. PSC motors can incorporate a less expensive type of laminations since a lower. grade steel may be used with a silicon content. Such laminations do not require heat treatment. However, there are many problems associated with providing a four-pole PSC motor in a narrow frame of a box fan. The primary problem is that the profile of the typical four-pole PSC motor is too thick to fit within the narrow box fan, due to the construction of the motor, the internal motor windings, and the casings used for such motors. Another main problem preventing manufacturers from placing a four-pole PSC motor in a narrow box fan is the difficulty of mounting the motor in the confined mounting space. Furthermore, the operating temperature of typical four-pole PSC motors places them in the UL Class B category.
Typical mounting of motors includes attaching a mounting plate to the back of the motor casing, and fastening the mounting plate to the internal mounting, such as the strut within the box fan. This type of mounting requires use of additional space in the fan housing, also making it impossible to mount a four-pole PSC motor in a narrow housing to provide necessary clearance between the bladed propeller and the front grill of the fan. Further, this type of mounting, with a separate mounting plate, requires additional manufacturing cost and time, and risks mis-alignment of the motor in the fan housing.
One attempt at mounting a motor without a mounting plate was contemplated in U.S. Pat. No. 5,430,338 issued to McMillan et al. (xe2x80x9cMcMillanxe2x80x9d). McMillan teaches sandwiching the stator core within upper and lower housing casings to facilitate construction of the electric motor. Sandwiching the stator core within the housings alleviates manufacturing problems associated with aligning and configuring the stator and rotor within the electric motor housing. However, the sandwiching technique taught in McMillan fails to resolve other problems as it only makes the motor""s profile wider.
Furthermore, the profile of a motor must not only be narrow enough to fit within the narrow box fan, but once the motor is mounted within the narrow box and equipped with a blade assembly and the protective grills, the product must pass the xe2x80x9cProbe Testxe2x80x9d to gain UL approval. The xe2x80x9cProbe Testxe2x80x9d by UL is a test that determines if the fan product possesses the necessary clearance between the front of the bladed propeller and the front grill of the fan housing. If the blade rotates in a position that is too close to the front grill, it is determined to be potentially dangerous for consumers, and will not obtain UL approval. Generally, this test includes operating the fan while pushing a probe against the front grill with a given amount of force (one pound of force). Therefore, the fan motor must be mounted in a position that permits secure attachment of the blade assembly, without the blade assembly advancing too close to the front grill. It would be advantageous, therefore, to devise a structure for such a box fan with a four-pole PSC motor that may be mounted in a relatively narrow space, while keeping the bladed propeller away from the front grill.
Another problem with using a four-pole PSC motor in a narrow space within a fan is the relatively large thickness of such motors. The typical four-pole PSC motor has the bulk of its copper windings positioned on either of the sides of the laminations, thereby requiring additional thickness to them as compared to shaded pole motors. Further, by current UL standards, a clearance space of at least 2.4 millimeters (mm) is required between the copper windings and the cast metal outer casing of the motor. It would be advantageous, therefore, to develop a four-pole PSC motor that has a relatively reduced thickness, without compromising the volume of space required for the copper windings or violating:the UL standards of required clearance between the windings and the metal motor casing.
Yet another problem with attempting to make a box fan with a four-pole PSC motor is the fact that most four-pole motors operate at a higher peak torque than what is desirable for such a product. The peak torque of such motors typically resides at about 1200 revolutions per minute (RPM), whereas the peak torque output optimal for a box fan product is approximately 1000 RPM.
Therefore, there is a need for a fan with a four-pole PSC electric motor that has a narrow profile and runs at a lower temperature and peak torque output.
It is an object of the present invention to provide a narrow box fan with a four-pole PSC electric motor in which the four-pole PSC motor is narrow enough to fit within the narrow box fan.
It is another object of the present invention to provide a narrow box fan having a four-pole PSC motor in which a portion of the casing of the motor is recessed in order to elongate the exposed portion of the output shaft to reduce the width of the motor and blade assembly.
It is a further object of the present invention to provide a narrow box fan in which the motor has legs which extend off the sides of the rear casing for securely mounting to parallel brackets on the rear grill of the fan.
It is still a further object of the present invention to provide a box fan with a four-pole PSC motor in which the laminations are sandwiched by the casings, and the inner dimensions of the casings are wider than the windings so that wiring may pass through the casings through the side of the motor rather than the rear of the motor, thereby reducing the overall width of the motor, and wires may pass along the side of the copper windings.
It is another object of the present invention to provide a narrow box fan having a four-pole PSC motor in which the windings of the motor are spread out in the radial direction and reduced in the axial dimension, thereby reducing the overall width of the profile of the motor.
It is another object of the present invention to provide a narrow box fan having a four-pole PSC motor in which the outer diameter of the windings of the motor extends beyond the outer diameter of the stator slots, whereby efficiency is enhanced and the width of the motor profile is reduced.
It is yet another object of the present invention to provide a narrow box fan in which the vented casings may be placed close to the windings, and in particular, in which the casings are made of plastic, and thus may even be in close proximity or in direct contact with the windings, thereby reducing the width of the motor and improving ventilation for greater efficiency.
It is another object of the present invention to provide a narrow box fan with a four-pole PSC motor in which a portion of the stator slots is flattened, whereby efficiency is improved.
It is a further object of the present invention to provide a narrow box fan with a four-pole PSC motor in which the peak torque of the motor is approximately 1000 rpm.
The present invention is directed to a fan having a four-pole PSC electric motor and a housing for shielding the electric motor. The electric motor comprises a rotor and a stator. The stator includes a core of stacked laminations having a first supporting surface defined by a first outermost lamination and a second supporting surface defined by a second outermost lamination. Copper windings are wound about the stator. The rotor includes an output shaft.
The housing comprises front and rear casings. The casings are generally dome-shaped and centered about a longitudinal axis. The first casing has an interior surface and an exterior surface. The interior surface defines a first chamber. The exterior surface comprises a circumferential side wall connected to a first vented end wall. The first vented end wall has a recessed central area which extends inwardly toward the stacked lamination. The recessed central portion defines a central opening through which the output shaft of the electric motor passes.
The rear casing also has an interior surface and an exterior surface. The interior surface defines a second chamber. The exterior surface comprises a second circumferential side wall connected to a second vented end wall.
The casings are wider in diameter than the stator coils to allow for ventilation, and side entry and passage of lead wires, yet narrow enough in diameter such that aluminum die casting of the casings is feasible.
Other features and advantages of the invention will be apparent from the following specification taken in conjunction with the following drawings.